For me part of the issue is that I have enough money troubles where I am in life (and I'll admit Coin isn't probably targeted at me in that case) that I don't have time to worry about there being issues with the device that delivers purchases. I don't need, for example, one of those issues being that something that should hit a credit card hits a debit card or vice versa. When I give someone plastic they can't change the payment account when I'm not looking.